Construction of Web-GIS in San'in region for integrating geophysical survey data with geotechnical information

Constructing a database of information on geotechnical information, such as geophysical survey results and borehole data, and sharing it among researchers and practitioners will be useful for the development of subsurface research and the prevention of disasters such as earthquakes and landslides. In earthquake disaster prevention, geotechnical information is particularly important for strong ground motion prediction. The geotechnical information includes analysis results based on geophysical surveys and seismic observations, and borehole data. These databases can be displayed on a map using GIS, and the existing analysis results can be checked sequentially. This will allow us to consider new observation plans and to improve the efficiency and accuracy of the analysis of the subsurface structure model. In this study, a database of geotechnical information was constructed for the San-in region. The database of geotechnical information includes the results of microtremor and gravity survey, analysis of ground structure by seismic observation, and borehole data in Tottori and Shimane prefectures. In addition, we constructed a system to display the constructed database on a map in a web browser (Web-GIS). For the base system of the GIS, Leaflet, a Java Script library, was used to display the prepared database of geotechnical information using the GSI tiled map as the base map. The developed database and GIS system will be used to researchers and the public in the future.

Strong Ground Motion Prediction Model for PGV and Spectral Velocity for the Chilean Subduction Zone

ABSTRACT Ground-motion prediction models (GMPMs) are a critical tool in performing seismic hazard analyses; in turn, these studies condition structural designs. Consequently, new research has appeared not only with a regionalization focus but has also explored the prediction of intensities other than acceleration. We present a GMPM for peak ground velocity (PGV) and spectral velocity (Sv) for the Chilean subduction zone. Because of the limitations of VS30 as site proxy, the proposed model adds the site’s fundamental frequency (f0) as an explanatory variable for the site term in the GMPM. We developed the model for PGV and spectral response periods between 0.06 and 10 s. The total error (σ) of the model shows a slight reduction with the inclusion of the fundamental frequency (f0) compared with a similar model for the pseudoacceleration response spectrum in the same zone. We used the proposed model to predict structural damage during the 2010 Mw 8.8 Maule earthquake, showing a good fit with the geographical distribution of damage, and this creates an opportunity to characterize the seismic behavior of soil deposits, including basins, for urban planning.

Inversion of Love waves in earthquake ground motion records for two-dimensional S-wave velocity model of deep sedimentary layers

We propose a new waveform inversion method to estimate the 2D S-wave velocity structure of deep sedimentary layers using broadband Love waves. As a preprocessing operation in our inversion scheme, we decompose earthquake observation records into velocity waveforms for periods of 1 s each. Then, we include in the inversion only those periods for which the assumption of 2D propagation holds, which we propose to determine through a principal component analysis. A linearized iterative inversion analysis for the selected Love wave segments filtered for periods of 1 s each allows a detailed estimation of the boundary shapes of interfaces over the seismic bedrock with an S-wave velocity of approximately 3 km/s. We demonstrate the effectiveness of the technique with applications to observed seismograms in the Kanto Plain, Japan. The differences between the estimated and existing velocity structure models are remarkable at the basin edges. Our results show remarkable differences from previous existing structural models, particularly near the basin edges while being in good agreement with the surface geology. Since a subsurface structure at a basin edge strongly affects the earthquake ground motions in a basin with the generation of surface waves, our method can provide a detailed model of a complex S-wave velocity structure at an edge part for strong ground motion prediction.

Inversion of Love Waves in Earthquake Ground Motion Records for Two-dimensional S-wave Velocity Model of Deep Sedimentary Layers

We have proposed a new waveform inversion method to estimate a 2D S-wave velocity structure of deep sedimentary layers using broadband Love waves. As a preprocessing operation in our inversion scheme, we decompose earthquake observation records into velocity waveforms at periods of 1 s interval. Then, we verify an assumption of 2D propagations of Love waves with polarization features based on a principal component analysis to select the segments applied for the inversion. A linearized iterative inversion analysis for the selected Love wave segments filtered at period of every 1 s allows a detailed estimation of boundary shapes of interfaces over the seismic bedrock with an S-wave velocity of approximately 3 km/s. We demonstrate the technique’s effectiveness with applications to observed seismograms in the Kanto plain, Japan. Differences between the estimated and existing structural models are remarkable at basin edges. A regional variation of the near-surface S-wave velocities in our model is similar to a distribution of surface geological classifications. Since a subsurface structure at a basin edge strongly affects earthquake ground motions in a basin with generations of surface waves, our method can provide a detail model of a complex S-wave velocity structure at an edge part for a strong ground motion prediction.

Modeling of Subsurface Velocity Structures from Seismic Bedrock to Ground Surface in the Tokai Region, Japan, for Broadband Strong Ground Motion Prediction

For sophistication of strong ground motion prediction in terms of disaster mitigation, one of the principal issues is to model subsurface velocity structures so that characteristics of earthquake ground motions can be reproduced in the broadband range 0.1 Hz to 10 Hz. In recent years, subsurface structures have been modeled in sedimentary layers on seismic bedrock for a few regions of Japan, in a national project. In this study, subsurface velocity structures were modeled from seismic bedrock to the ground surface for the Tokai region. These models were constructed in accordance with the subsurface velocity structure modeling scheme published by the Headquarters for Earthquake Research Promotion. To begin with, initial models were constructed based on existing bore-hole data, geological information, etc. Next, they were improved based on results of microtremor explorations which had been conducted in recent years. It was found that the new model had different characteristics to the conventional model. This paper will present the modeling process and characteristics of distribution maps for velocity structures and amplification index.

Source Modeling for Predicting Ground Motions and Permanent Displacements Very Close to the Fault Trace

A conventional “recipe” for strong ground motion prediction has been applied to the seismic fault (deep fault; located within seismogenic layer). In order to perform assessments of strong ground motions and permanent displacements at sites very close to the fault trace, we proposed the method of modeling that takes the entire ruptured fault from the ground surface to the seismic fault into account. Our approach was validated by the simulation of observed records obtained at stations very close to the fault trace of the mainshock of the 2016 Kumamoto Japan, earthquake (Mw7.1). Also, through the ground motion assessment performed for a hypothetical strike-slip fault with a 90[Formula: see text] dip angle, we found that adding the shallow fault had virtually no effect on acceleration time history, but it had a clear effect on the fault-parallel component of velocity and displacement time histories in the area close to the fault trace.